Question

The output voltage of a voltage amplifier has been found to decrease by 20% when a load resistance of 1 k is connected. What is the value of the amplifier output resistance?

Answer 1

We use the voltage division problem between the load resistance, amplifier output resistance as

`V_(out) = V_(amlifire) * (R_(load) )/(R_(load) + R_(out) )`.

Here,
`V_(out)` is the output voltage,
`V_(amlifire)` is the amplifier voltage,
`R_(load)` is the load resistance and
`R_(out)` is the amplifier output resistance.

Therefore,

`1-(20)/(100) = (1 \ k\Omega )/(1 \ k\Omega +R_(out) ) \\\\ R_(out) = (1 \ k\Omega )/(0.8) -1 \ k\Omega =1250 \Omega -1000 \Omega =250 \Omega`.

Thus, the amplifier output resistance is
`250 \ \Omega`.